embedded non volatile memories for consumer applications...
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Embedded Non Volatile Memories for Consumer Applications:Status and Perspectives
Paola Zuliani
Workshop on Innovative Memory Technologies
Grenoble, June 21st 2012
Outline
• Embedded Non Volatile Memory• Challenge and Opportunity
• Status
• Emerging Technologies• Key Features
• Applications
• ePCM Overview
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27/06/2012Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
Outline
• Embedded Non Volatile Memory• Challenge and Opportunity
• Status
• Emerging Technologies• Key Features
• Applications
• ePCM Overview
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27/06/2012Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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eNVM Applications
Industrial MCU
Home Entertainment
Powertrain Smart CardsMedical
Domotics
Two key functions• Code Execution• Data Management
Car Body
Safety
DIS
Automotive Consumer
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
eNVM Market
• Industrial and automotive applications are the most important segments
• MCU market size is expected to grow, as well as the NVM content per MCU
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K.Baker, Freescale (IMW 2012)
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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eNVM Market Challenges
• Market trends impose severe challenges to embedded Non Volatile Memories
• Major factors• Price Erosion
• Fast Program/Erase operation needs
• Low Power Supply operating conditions
• High cycling capability
• Retention
• Granularity (capability to erase/program Byte or Word)
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
eNVM Technology Challenges
• Cell Scalability
• Cost
• Performance
• Power Consumption
• Reliability
Different ranking of the above parameters depending on the specific application
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27/06/2012Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
Today eNVM Solutions• EEPROM
+ Low Power � P/E by Fowler Nordheim
+ Reliability
- Cell Size � 2T architecture
- 15V Operation
+ Bit granularity
• FLASH NOR- Low Power � Programming by Hot Carrier
+ Reliability
+ Cell Size
- 10V Operation
- Sector/ page granularity
• FLASH Split-Gate+ Low Power programming � SSI
- Endurance granted by design
- Cell Size � 1.5T
- Process Complexity
+ Page granularity
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Low-End productsi.e. mainly driven by cost
High-End productsi.e. mainly driven by performances and/or reliability
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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Low Power productsi.e. mainly driven by low power consumption
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FG Limiting Factors• FG cell scalability is achieving its limits
• Reduced cell current at each techno step � difficult sensing operation between different cell states
• Reduced coupling factors � increased internal voltage generation to compensate
• FG Program/Erase operations increase internal complexity
• Flash requires the usage of complex verify algorithm
• EEPROM requires very high internal voltage to activate the cell
• Design solution for Low Power Supply embedded products
• Byte or word alterability is still an added value
• FG is not a universal solution
• EEPROM or Flash are used according to the application
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
Outline
• Embedded Non Volatile Memory• Challenge and Opportunity
• Status
• Emerging Technologies• Key Features
• Applications
• ePCM Overview
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27/06/2012Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
Emerging Technologies: the eNVM case
• FG solution is difficult to integrate with high-K metal gate technology for advanced CMOS
• Due to very different applications a single cell/architecture can hardly cover all the needs
• New technologies look-up is essential for the leadership in the eNVM world
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Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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Emerging eNVM
• Key factors• Easy to integrate into the
baseline logic platform
• Suitable to fit application requirements
• Cost
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• Guidelines• Integration in the Back-End of the
process (after contact definition)• Compact cell area• No impact on CMOS
• Reliability and Low Power• Wide range of applications• Automotive (Zero Defect requirements)
should rely on volume production, possibly for Stand-Alone memories (same as today FLASH route)
• Few additional masks
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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eNVM Applications
Industrial MCU
Home Entertainment
Powertrain
Smart Cards
Medical
Domotics
Car Body
Safety
DIS PCMPCMFeRAM
MRAM
RRAMRRAM
STRAMSTRAM
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
From MRAM to STRAM (1/2)14
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MRAM STRAM STRAM PMA
2000 2008
• MRAM• Assessment of field MRAM for High Reliability applications
(16Mb, 1.42µm2 cell size at 180nm node, IBM 2004)• Need read before write• Poor scalability below 90nm
• STRAM• Perpendicular Magnetic Anisotropy (PMA) materials mandatory for low write current• ∆R/R ~200% to be compatible with CMOS � very low reading window available for
memory industry• Trade-off between low write current density and thermal stability• STRAM technology is challenging (very complex multi-layer stack)
year
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
From MRAM to STRAM (2/2)
• Nevertheless there is an increasing interest from industry…
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27/06/2012Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
RRAM (1/2)
• The Resistance change is due to formation and dissolution of a conductive filament in a dielectric layer
• Three categories1. Unipolar systems (thermally assisted, very high current)
2. Bipolar Conductive Bridge (CBRAM): electrochemical dissolution and re-deposition of an active electrode
3. O-RRAM: based on movements of Oxygen anions
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(2) (3)R.Waser , IEDM 2011 Tutorial
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
RRAM (2/2)
• RRAM represents one of the most interesting technology solution for alternative eNVM - especially for Low Power applications
• Nevertheless, storage mechanism is not fully understood
• Reliability assessment of RRAM technology is far from maturity level reached on PCM
• Long-term reliability (solid extrapolation at 10y)
• Retention vs write power
• Trade-off between cycling and HTDR
• Behavior at very high temperature (>100C)
• Some hints but no data on scalability
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Outline
• Embedded Non Volatile Memory• Challenge and Opportunity
• Status
• Emerging Technologies• Key Features
• Applications
• ePCM Overview
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27/06/2012Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
New Materials: Past and Future19
Semiconductor industry has been driven by introduction of new materials over decades
1980s1990s2000s2010s
Chalcogenide Alloys over Decades
• Reference Phase Change material for memories is Ge2Sb2Te5
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1970 1990 2000
Xerography RW DVD-CD Memories
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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ePCM Competitive Advantage
• Easier to be integrated with advanced logic• lower voltage• no impact on CMOS front-end
• Cost-effective• few additional masks (only 3 masks overhead for storage element
definition)• smaller cell vs. EEPROM, smaller over-head vs. FLASH
• Better performance• single bit over-write• programming speed• endurance
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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PCM array Logic
Stacked contacts
Memory Architecture
A true 3D integration of Non Volatile Memory
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
23ePCM Outlook
• PCM is the most mature among novel memory concepts• Micron and Samsung starting stand-alone memory production at 45nm
• Embedded PCM Technology is developed in synergy with stand-alone mainstream
• Same storage element, with MOS as selector
• Feasibility at 90nm node demonstrated for consumer applications
• Embedded PCM can be a real breakthrough for process cost saving and performances
• NVM integrated in BEOL
• Best in class for power consumption and write data throughput, perfectly fitting contact-less secure microcontrollers requirements
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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ePCM Status
High level of confidence in terms of:
• Yield• ~90% on 4Mbit Test Chip (with redundancy)
• Reliability• 10y retention at 85C granted• >10M cycles cell level• 1ppm defectivity after 100k cycles: solid data collection on 4Mb
• Storage Mechanism• Retention vs write power• Failure modes
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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ePCM Reliability
• Less critical than FLASH memory in terms of
• Cycling at High Temperature
• Retention after cycling
• Extended endurance
• New retention concept
• It is a matter of probability for crystallization
• No “weak” bits in the array
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Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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e-PCM integration – 4Mbit Test Chip
• A 4Mbit Test Chip integrated in 6 metal levels 90nm process for extrinsic evaluation of e-PCM cell
Selector
PCM material
Heater
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
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Set and Reset Distributions
• A strong cell-level signal (3 decades change in resistance) must be translated in reading window in the µA region
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Ref. Current
16µA
Read Window
25µA
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
ePCM for Low Power
• Thanks to• Medium Voltage operation (<3.3V)
• Very fast Reset operation (<100ns)
• Low current Set operation (~Ireset/2)
• Low Voltage Read operation (<1.2V)
• GO1 Row/Column decoder
• Bit alterability (no need of Erase before Program)
• ePCM solution results best-in-class in terms of• Electrical performances (access time, consumption, throughput)
• Capability to achieve aggressive contact-less requirements
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Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
ePCM Cell
• ePCM Cell is defined by:• Circuitry rules in Y direction
• Reset current in X direction
• Aggressive cell area in the range of 18F2 can be obtained• Still room for improvement with proper GST optimization, e.g. by doping
• Cell scalability granted for next technology nodes (65nm,45nm and beyond)
• Very compact macrocell results from small circuitry overhead needed for row/column decoder, charge pumps, no recovery algorithms
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Y
X
Source Line
Word Line
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
Materials Customization for ePCM 30
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Sb
Ge Te
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GST 225 ���� 22% Ge 22% Sb 55% Te
• Commonly used Ge2Sb2Te5 has crystallization temperature close to 150C:
• No way to preserve code content after soldering (2min at 260C)
• Big challenge and refresh concept to fit automotive specs (some years HTDR at 150C)
• By modifying the percentage of Ge-Sb-Te in the alloy, crystallization temperature ranging from 150C up to 400C have been obtained
• Customization of material inside ternary diagram is feasible (i.e. retention, SET speed or programming current)
Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives
Conclusions (1/2)
• MCU market size is expected to grow, as well as the NVM content per MCU, so representing an important business opportunity
• By considering scaling trends, FG solution seems difficult to integrate with high-K metal gate technology for advanced CMOS
• Among emerging technologies, the whole family of RRAM and the STRAM appear particularly appealing (in particular, CBRAM seems promising for Low Power applications)
• Nevertheless, it is a long journey towards a reliable industrial solution…
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Conclusions (2/2)
• PCM is the most mature among novel memory concepts (production started at ~Gb densities and ~45nm technology node)
• Embedded PCM Technology is developed in synergy with stand-alone mainstream and can be a real breakthrough for process cost saving and performances
• Major progress in Materials Exploration activity• 10 years HTDR at T>150C demonstrated cell level
• Good confidence to overcome soldering limitations
• Key features for Low Power applications confirmed
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Acknowledgments
• The whole Team (process, device, reliability) working on ePCM development
• Micron Process R&D Team of Agrate Brianza
• R.Annunziata, A.Maurelli, A.Conte for valuable suggestions
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27/06/2012Embedded Non Volatile Memories for Consumer Applications: Status and Perspectives